PHOTOCATALYTIC DEGRADATION OF TURQUOISE BLUE DYE USING IMMOBILIZED AC/TIO2: OPTIMIZATION OF PROCESS PARAMETERS AND PILOT PLANT INVESTIGATION

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1 Journal of Engineering Science and Technology Special Issue on SOMCHE 2014 & RSCE 2014 Conference, January (2015) School of Engineering, Taylor s University PHOTOCATALYTIC DEGRADATIO OF TURQUOISE BLUE DYE USIG IMMOBILIZED AC/TIO2: OPTIMIZATIO OF PROCESS PARAMETERS AD PILOT PLAT IVESTIGATIO JUREX C. GALLO 1, *, MARTI B. MARIAO 1, ALTO D. LUCAAS 1, MICHAEL B. KO 1, JOSEPHIE Q. BORJA 1, H. HIODE 2, SUSA M. GALLARDO 1 1 Chemical Engineering Department, De La Salle University, Taft Avenue, Manila, Philippines 2 Tokyo Institute of Technology, Japan *Corresponding Author: jurex_gallo@yahoo.com Abstract AC/TiO 2 was synthesized via sol-gel method and characterized. Response Surface Methodology (RSM) based on Central Composite Design (CCD) was applied in optimization of process parameters in photocatalytic degradation of Turquoise blue dye (TBD) under UV light. The optimum conditions are mg/l initial dye concentration, initial solution ph of 3.00, 3.00 g/l catalyst loading, recirculating flow rate of 100 ml/s and UV intensity of 2.50 mw/cm 2. A 90.01% color removal of TBD and 86.4% color removal of textile wastewater with TBD under UV light were achieved while 38.5% color removal of TBD in textile wastewater was observed under visible light in 6-hour irradiation. In pilot plant investigation using a fixed-bed reactor, a 54.8% color removal of TBD in textile wastewater in 1.5 hours of solar irradiation was observed. Keywords: Photocatalytic treatment, AC/TiO 2, Textile wastewater, Optimization, Response surface methodology. 1. Introduction Photocatalytic degradation of dyes using TiO 2 has been studied in the past by various researchers [1]. There are different types of dyes used by textile industries. Turquoise blue dye (TBD), an azo dye with molecular formula C 32 H 16 8 S 2 O 6 Cua 2 and molecular structure shown in Fig. 1 belongs to direct dye which ranked next to acid dye in terms of persistency and is also the most persistent compared to basic dye, disperse dye and reactive dye when subjected to 64

2 Photocatalytic Degradation of Turquoise Blue Dye Using Immobilized omenclatures A Final absorbance A 0 Initial absorbance C Final dye concentration, ppm C 0 Initial dye concentration, ppm [Io] Light intensity, mw/cm 2 [TBD] Initial Turquoise blue dye concentration, ppm Abbreviations CCD RSM TBD Central composite design Response surface methodology Turquoise blue dye photocatalytic treatment using JT Baker TiO 2 [2]. Azo dyes can be grouped as monoazo, diazo, triazo or polyazo dyes according to the number of azo bonds ( = ) in the structure. The color of azo dyes is due to these azo bonds and the associated chromophores [3]. Cu (SO 3a) 0.5~2.5 (SO 3a) 0.5~2.5 Fig. 1. Molecular structure of TBD [4]. The objective of this study is to optimize the operating parameters in photocatalytic degradation of TBD using a recirculating reactor with immobilized AC/TiO 2 and facilitate the transfer of technology to an industry partner. The TiO 2 catalyst impregnated with AC was used in this study for its known synergistic effect in photocatalysis [5]. The operating parameters which include initial dye concentration, catalyst loading, initial dye solution ph, UV intensity and recirculating flow rate have been studied by previous researchers. Optimum parameter values vary depending on the target pollutant, type of catalyst and design of reactor used; hence, there is a need to evaluate optimum operating parameter values for every new photocatalytic dye degradation study. In the present study, Response Surface Methodology (RSM) was used in determining the optimum values of operating parameters in photocatalytic dye degradation using a recirculating photocatalytic reactor. Central Composite Design (CCD) as shown in Fig. 2 is a widely used RSM being applied in optimization and is useful for building a second order model for a response variable without needing to use a complete three-level factorial experiment. The application of photocatalysis in the treatment of textile wastewater is timely, as to date, no universal photocatalytic system that is commercially available which features high efficiency, easy catalyst activity and activates in visible light [6].

3 66 J. C. Gallo et al. Fig. 2. Central composite design for p = 2 factor. 2. Methodology 2.1. Laboratory investigation TBD is the target pollutant used in this study which was provided by the textile industry partner. The catalyst used in photocatalytic degradation of TBD is AC/TiO 2 composite catalyst with 8.72% wt AC loading synthesized via sol-gel method and calcined at 400 o C. In catalyst preparation via sol-gel, the materials used are Titanium isopropoxide, glacial acetic acid, double distilled water and activated carbon acquired from Carbo Karn Co. Ltd. in Thailand. The catalyst produced was characterized for its BET surface area, pore size, pore volume, Point of zero charge (PZC), particle size, TiO 2 crystal structure and band gap. AC/TiO 2 was immobilized in glass plates using Polyethylene glycol (MW = 10,000 g/mol) as binder with further heat treatment for 3 hours at 300 o C. The photocatalytic reactor used in this study is the recirculating batch reactor shown in Fig. 3. The reactor has a 254-nm UV lamp and equipped with a quartz or a pyrex glass sleeves. The effective volume of the reactor is 1 L. The temperature of the solution is maintained at 32.0 ± 0.5 o C by cooling water that flows inside the sleeve of the UV lamp. Air was supplied into the dye solution by an air pump at 100 ml/s which maintained the solution saturated with oxygen. The catalyst-coated glass plates were installed in a sample holder designed to fit exactly at the bottom of the reactor hence prevents movement during photocatalytic reaction. The UV lamp is installed in a vertical position and the distance from the lamp to the surface of immobilized AC/TiO 2 is approximately 25 mm. The body of the reactor was totally covered with aluminum foil to maximize the use of light within the vessel. The % color removal was calculated using Eq. (1): % Color removal= 100 (1) where = initial dye concentration and C = final dye concentration at 6 hours irradiation.

4 Photocatalytic Degradation of Turquoise Blue Dye Using Immobilized Fig. 3. Recirculating batch photocatalytic reactor Pilot plant investigation The pilot plant reactor (see Fig. 4) is a fixed bed, thin film type solar photocatalytic reactor adopted from oguiera and Jardim [7]. In this reactor, the textile wastewater was pumped and allowed to flow along the fixed bed of photocatalyst. The reactor used solar light to activate the AC/TiO 2 film. The exposure of wastewater to sunlight was carried out from 9 AM until 3 PM. The parameters evaluated are shown in Table 1. Fig. 4. Fixed bed pilot plant reactor Table 1. Parameter values in pilot plant investigation. Parameter (Unit) Values Flow rate (ml/min) 167, 222, 333 o. of recirculation passes 1, 2, 3 Residence time (hours) 1.5, 2.0, 3.0

5 68 J. C. Gallo et al. 3. Results and Discussions 3.1. Laboratory investigation Table 2 summarizes the characterization results of immobilized AC/TiO 2. AC/TiO 2 with 8.72% wt AC loading has a BET surface area of m 2 /g and with pure anatase crystal structure of TiO 2. The AC/TiO 2 particles are in nanometer size and have a band gap of 3.33 ev which indicates that the catalyst has no visible light absorption. The PZC of the catalyst is As TBD is anionic azo dye, effective adsorption of dye molecules onto the surface of AC/TiO 2 is expected at acidic ph of dye solution. Table 2. Characteristics of AC/TiO 2 catalyst. Parameter (Unit) Value BET surface area (m 2 /g) Pore volume (cm 3 /g) Pore size (Å) % weight AC (%) 8.72 Particle size (nm) 9.46 band gap (ev) 3.33 Point of zero charge 7.20 TiO 2 structure Anatase Meanwhile, results of photolysis and dark adsorption experiments as shown in Figs. 5 and 6 show a color removal of 3.93% and 21.7% respectively. These experiments were performed to ensure that color removal in later experiment is mainly due on photocatalytic reaction. Fig. 5. Photolysis [TBD O ] = 15mg/L, ph = 3.0, Io = 2.5 W/cm 2. Fig. 6. Adsorption. [TBD O ] = 15 mg/l, ph = 3.0, AC/TiO 2 loading = 3.0 mg/l.

6 Photocatalytic Degradation of Turquoise Blue Dye Using Immobilized An approximate function of % color removal based on experimental results was evaluated using the Design Expert software and is given below: Color Removal (%100) = A B C D E AB AC AD AE BC BD BE CD CE DE AA BB CC DD EE (2) where, A = Initial dye concentration, ppm B = Catalyst loading, mg/l C = Initial dye solution ph D = UV intensity, mw/cm 2 E = Recirculating flow rate, ml/s From the derived mathematical model, the AOVA (see Table 3) showed an F-value of which suggests that the model is significant. All model terms i.e. initial dye concentration, catalyst loading, initial dye solution ph, UV intensity and recirculating flow rate are significant with Prob>F values <0.05. The predicted R-squared of 0.71 is a reasonable agreement with the Adj R-squared of This model has an adequate precision greater than 4.00 which shows that it is desirable and indicates an adequate signal. F-values implied that the initial dye concentration has the highest influence in color removal among the other parameters involved. Source Table 3. AOVA for response surface quadratic model. Sum of Squares Df Mean Square F- value P-value Prob>F Model < A- initial dye concentration < B- catalyst loading < C- initial dye solution ph < D- UV intensity < E - Recirculating flow rate Residual E Lack of fit E Standard deviation Mean 0.50 R- squared 0.93 Adjusted R- squared 0.88 Predicted R-squared 0.71 Adequate precision The effect of operating parameters showed that the color removal increases when either or both the catalyst loading and UV intensity is increased. However, the color removal decreases as the initial dye concentration, initial

7 70 J. C. Gallo et al. solution ph and recirculating flow rate increases. The increase in photocatalytic efficiency as the UV intensity is increased is due to the enhanced production of hydroxyl radicals. Also, the increase in the amount of catalyst increases the active sites on the photocatalyst surface thus causing an increase in the number of OH radicals which can take part in the discoloration of dyes. On the other hand, as the initial concentration dye increases, the equilibrium adsorption of dyes on the catalyst surface active sites also increase, hence competitive adsorption of OH on the same site decreases. This means a lower formation rate of OH radical responsible for dye degradation [8]. Also, as the initial dye concentration increases, the path length of photons entering the solution decreases, which result in lower photon adsorption on catalyst particles, and consequently lower photocatalytic reaction rates [9]. Moreover, as the recirculating flow rate increases, the percentage color removal decreases. This result suggests the significance of contact time of catalyst and the target pollutant. The optimum conditions and full factorial central composite design showing the actual and predicted values are presented in Table 4 and Table 5 respectively. In Table 5, the color removal of TBD at optimum conditions in 6 hour-irradiation is 90.01%. Table 4. Optimum conditions Parameter (Unit) Value Initial dye concentration (ppm) 15 Catalyst loading (g catalyst/l solution) 3.00 Initial dye solution ph 3.00 UV intensity (mw/cm2) 2.50 Recirculating flow rate (ml/s) 100 Optimum conditions were used in photocatalytic degradation of textile wastewater with TBD under UV light and the result shows 86.40% color removal in 6-hour irradiation. This suggests that other chemicals present in actual textile wastewater may affect the efficiency of the catalyst. Moreover, photocatalytic degradation of textile wastewater with TBD was also performed under visible light and the result shows 38.5% color removal in 6-hr irradiation (see Fig. 7) with corresponding COD removal of %. Fig. 7. Photocatalytic removal of TBD in textile wastewater under visible light.

8 Photocatalytic Degradation of Turquoise Blue Dye Using Immobilized Table 5. Optimization results of full factorial central composite design. Run o. Dye Concentration Catalyst loading Dye solution ph UV intensity Recirculating Flow rate Actual % Color Removal Predicted % Color Removal Pilot plant investigation Using the optimum conditions determined in the laboratory, results of pilot plant investigation (see Fig. 8) shows that the 1.5-hour residence time achieved the highest color removal of 54.8%. More number of circulations passes (3 passes) resulted to a higher dye degradation. The best recirculation flow rate is ml/min in which the residence time is 1.5 hours. It can also be observed (see Table 6) that as the intensity of solar light decreases, the % color removal also decreases. Other monitoring results show that both the ph and the temperature rise in the progress of photocatalytic experiments. The percentage color removal observed in pilot plant investigation (54.80%) which exceeds the result obtained in laboratory investigation (38.50%) can be ascribed to the approximately 10% UV spectrum in solar light where the AC/TiO 2 is mainly applicable. The higher intensity of solar light (687 mw/cm 2 ) during pilot plant investigation compared to the light intensity used in laboratory

9 72 J. C. Gallo et al. investigation (2.50 mw/cm 2 ) also contributed to the increase in the efficiency of AC/TiO 2. Moreover, the improved contact between the AC/TiO 2 film and the pollutant in the fixed bed reactor also led to the better performance of the catalyst. Fig. 8. Pilot plant investigation results. Parameter (Unit) Table 6. Summary of results. Weather status Average Sunlight Intensity A/A o % Color Removal (Absorbance) % PCU reduction 2 hours, 1 pass Sunny hours, 2 pass Sunny hours, 3 pass Sunny/ cloudy hours, 1 pass Sunny hours, 2 pass Sunny hours, 3 pass Cloudy/ sunny hour, 1 pass Cloudy hour, 2 pass Cloudy hour, 3 pass Cloudy/ sunny Conclusions The following are the conclusions derived based from the results: The immobilized AC/TiO 2 with 8.72% weight AC loading has a BET surface area of m 2 /g and with pure anatase crystal nanosized TiO 2. In laboratory investigation, the model derived for this system is significant with an F-value of The initial dye concentration has the highest influence in color removal. Moreover, 90.01% color removal for TBD while 86.40% color removal of actual textile wastewater was observed during photocatalytic treatment under UV light. However, only 38.50% color

10 Photocatalytic Degradation of Turquoise Blue Dye Using Immobilized removal in 6-hr irradiation was achieved using visible light with corresponding COD removal of 42.52%. In the pilot plant investigation, 54.80% color removal was observed in 1.5 hrs residence time with 3 recirculation passes. The approximately 10% UV spectrum in solar light, higher light intensity and improved contact between the catalyst and textile wastewater in the fixed bed reactor contributed to the enhanced photocatalytic efficiency of AC/TiO 2. Acknowledgment The authors gratefully acknowledge the Engineering Research and Development for Technology (ERDT) of the Department of Science and Technology (DOST) for the financial support provided in the project. Likewise, sincere appreciation was also extended to De La Salle University- Manila, Tokyo Institute of Technology, Burapha University and Saffron Philippines Incorporated. References 1. Behnajady, M.; Daneshvar,.; and Rabbani, M. (2007). Photocatalytic degradation of CI Red 27 by immobilized ZnO on glass plates in continuousmode. Journal of Hazardous Materials, 140(1), Gallo, J.; Mariquit, E.; Co, R.; Borja, J.; and Gallardo, S. (2008). Assessment of the colored wastewater treatment in the Philippine textile industry and preliminary study on the color removal of wastewater using photocatalysis. Manila, Philippines. 3. Janus, M.; Kusiak, K.; Choina, J.; Ziebro, J.; and Morawski, A. (2009). Enhanced adsorption of two azo dyes produced by carbon modification of TiO 2. Desalination, 294(1), Liu, S.; Chen, X.; and Chen, X. (2007). A TiO 2 /AC composite photocatalyst with high activity and easy separation prepared by a hydrothermal method. Journal of Hazardous Materials, 143(1), Arana, J.; Dona-Rodrigues, J.; Rendon, E.; Cabo, C.; Gonzales-Diaz, O.; Herrera-Melian, J.; Perez-Pena, J.; Colon, G.; and avio, A. (2008). TiO 2 activation by using activated carbon as a support Part I. Surface characterisation and decantability study. Applied Catalysis B: Environmental, 44(2), Han, F.; Kambala, V.; Srinivasan, M.; Rajarathnam, D.; and aidu, R. (2008). Tailored Titanium dioxide photocatalysts for the degradation of organic dyes in wastewater treatment: A review. Applied Catalysis A: General, 359(1), oguiera, R.; and Jardim, W. (1996). TiO 2 fixed-bed reactor for water decontamination using solar light. Solar Energy, 56(5), Akyol, A.; Yatmaz, H.; and Bayramoglu, M. (2004). Photocatalytic decolorization of Remazol red RR in aqueous ZnO suspensions. Applied Catalysis B: Environmental, 54(1), Habibi, M.; and asr-esfahani, M. (2007). Preparation, characterization and photocatalytic activity of a novel nanostructure composite film derived from nanopowder TiO 2 and sol-gel process using organic dispersant. Dyes and Pigments, 75(3),